The present invention relates to the art of television cameras, and more particularly to the art of automatic registration of color television cameras.
Broadcast color television cameras usually utilize two or more image pick-up devices. Each of the different color components of the scene being imaged is focused on the imaging surface of a respective image pick-up device. Each pick-up device scans its respective imaging surface to produce a video signal corresponding to the image focused thereon.
The color video signals must be properly synchronized with one another so as to simultaneously convey information relating to the same portion of the focused image. Any missynchronization, or "misregistration", will result in the plural color components of the imaged scene being offset from one another in the image presented on a television screen.
The registration adjustments necessary to arrive at the desired synchronization of the video signals are usually done by automatic electronic circuitry. Registration control circuitry can be provided which functions continuously during the operation of the television camera. The circuitry senses features of the video signals which correspond to details of the imaged scene, and then adjusts the video signals so that the features occur simultaneously in time in the different video signals. Patents disclosing systems of this nature include Monahan, U.S. Pat. No. 4,053,203 and Dischert et al., U.S. Pat. No. 3,830,959.
Recently, digital processing circuitry has been employed to initiate and complete the registration of the video signals during a "set-up" period prior to normal use of the camera. The camera is focused on a prearranged test chart having a white background with various well-defined indicia marked thereon. The indicia produce prominent features in the video signals generated by the camera which can then be readily detected and used by a digital processing system to determine the magnitude and direction of registration error. The same video signals are used to detect and match the horizontal and vertical sizes of the rasters scanned by the individual pick-up tubes, as well as to detect and correct for other things such as skew and nonlinearity. The patent to Astle et al., U.S. Pat. No. 4,234,890 discloses a system of this nature. Cameras are sometimes designed to include integral test chart projectors, referred to as "diascopes".